I found an article, dated 10/31/2022 and published by Penn State’s College of Agricultural Sciences, that addresses the desirable concentrations of micronutrients for plants.
It isn’t cannabis-specific, but it includes this informative table (I had to shrink it to fit in one screenshot, but it’s legible when zoomed):
Full article: https://extension.psu.edu/interpreting-irrigation-water-tests
BTW, 1 mg/L is very nearly = 1 ppm.
After checking with our local water treatment plant, I learned that, these days, our water contains 70 ppm calcium and 30 ppm magnesium. That means I have no need to add cal-mag.
I’ve also found the table below, at this link.
For the nutrients that can be compared directly (i.e., nitrogen, silicon, iron, manganese, boron, and molybdenum), the tables agree pretty well.
The second table expresses recommended amounts of the other nutrients as a percentage of the soil’s cation-exchange capacity (CEC). That information isn’t very helpful because the only way to determine your soil’s CEC is to send it to a lab.
Wikipedia has a table that shows seven US soils that have CECs ranging from 3.5 to 138; further, CEC varies with pH. So, there may not be a good “typical” value to assume. On the other hand, it’s possible that the CECs of soils best-suited for cannabis tend to fall in a narrow range, but I don’t know what it is.
